1. Field of the Invention
This invention relates to engine aftertreatment systems and more particularly relates to apparatus, systems and methods for determining catalyst bed temperatures in engine aftertreatment systems designed to experience high temperature events.
2. Description of the Related Art
Environmental concerns have motivated the implementation of emission requirements for internal combustion engines throughout much of the world. Governmental agencies, such as the Environmental Protection Agency (EPA) in the United States, carefully monitor the emission quality of engines and set acceptable emission standards, to which all engines must comply. Generally, emission requirements vary according to engine type. Emission tests for compression-ignition (diesel) engines typically monitor the release of diesel particulate matter (PM), nitrogen oxides (NOx), and unburned hydrocarbons (UHC). Catalytic converters implemented in an exhaust gas after-treatment system have been used to eliminate many of the pollutants present in exhaust gas.
Many catalytic systems used in engine aftertreatment require periodic high temperature events to maintain the system. For example, a catalytic soot filter may require periodic regeneration events at a high temperature to oxidize soot from the filter. A catalytic system to adsorb NOx may require high temperature events to drive adsorbed NOx off of the catalytic substrate. Some catalysts adsorb sulfur oxides (SOx) during operation, and require very high temperature events to drive the SOx back off of the catalyst.
A catalytic component that reaches temperatures that are too high may experience degradation or failure. The catalyst can be degraded, the component may crack from thermal stresses, or the oxidation of soot may occur too quickly and cause a thermal event. In some cases, the temperature required to achieve a successful regeneration event may be close to the temperature which causes component failure. Thus, an accurate estimate of the physical catalyst bed temperature is required, or component operation and reliability may be jeopardized.
In the current art, an accurate estimate of the physical catalyst bed is difficult to achieve. Available temperature sensors have slow response times and cannot be easily embedded within the catalyst bed. In one example indicative of the current art, a temperature sensor is placed in each location, upstream and downstream, of the catalyst bed and a weighted average between the two sensors is used to estimate the catalyst bed temperature. The temperature may be offset by a temperature (e.g. +50 degrees Celsius) to account for the observation that internal bed temperatures may often be higher than either the upstream or downstream temperature sensor reading. This setup requires either significant risk to the component, or a conservative temperature offset which decreases system efficiency and fuel economy, and may introduce a risk that regeneration is estimated to be successful when in fact regeneration is not achieved.
A full heat transfer and energy balance model, combined with inputs from the engine conditions, could be developed. However, such a model requires significant knowledge of the system that may not easily be available (e.g. the reflectivity of the exhaust pipe and the engine block to estimate radiation), that may vary considerably within applications in ways that cannot be understood at the design time of the model, and that require computing power far beyond the typical computing capabilities that are generally commercially available for engine controls.
From the foregoing discussion, it should be apparent that a need exists for an apparatus, system, and method for determining a catalyst bed temperature that achieves sufficient accuracy to achieve regenerations within a catalytic component without reaching component failure temperatures. Beneficially, such an apparatus, system, and method, would enable estimating the catalyst bed temperature with generally available sensors, system parameters, and computing power.